These are the ones I know of:
socks at topica dot com -- this was the list, but has not had any messages since October 2006. Perhaps the Yahoo lists have overtaken it.
sockknittingmachines at yahoogroups dot com -- a no-sales, no-flames list that tends to stay fairly technical. Great resources in the files, great place for information about retreats and conferences. The list has done sock-swaps in the past, I know because I ran one (grin ... table of socks is from that!)
sockknittingmachineswapshop at yahoogroups dot com -- the sister "for sale" list to sockknittingmachines. A good place to post "ISO" (in search of) requests, barter requests, and sock-machine related items for sale. Look for recently posted machines for sale, if you are shopping for a sock machine.
sockknittingmachine at yahoogroups dot com -- spun off from sockknittingmachines, lower traffic.
sockknittingmachinefriends at yahoogroups dot com - a spinoff from sockknittingmachines that welcomes NZAK owners and also allows for-sale postings. Great resources in the files and photos.
If you know of another, let me know! I love collection sock machine information.